The primary purpose is to continue ongoing work concerned with development of an intraoral test for cariogenicity of foods. The test is based on a sensitive method for measuring the permeability of surface enamel to iodide (Arch. Oral Biol. 22,599, 1977). Our findings show a marked increase in permeability (Pi) of plaque covered enamel after sugar rinses or chewing of sugar gum over a period of 1 to 3 hrs. Rapid recovery of increased permeability after intraoral exposure without sugar has also been observed. The test involves the use of blocks of bovine enamel covered with a plaque of S. mutans and carried in holderson a prosthesis. Different designs of the holder and the prosthesis will be studied in order to optimize procedures for testing liquid and solid foods. Plaques of S. mutans cultured at different pH within the ranges of 4.5 to 7.0 will also be investigated in order to determine conditions for obtaining plaques with maximal cariogenic potential. Once standardized, the capabilities and limitations of the test will be established. The procedures will also be used to investigate the effect of various fluoride treatments on the sugar-plaque-enamel system and on the process of remineralization.